Food Tests

Linked to B2: Organisation

Aim

Test food samples for the presence of glucose (reducing sugar), starch, protein and lipid.

Practical Guide

Method & analysis

Exam Questions

Past-paper style

Mark Scheme

Model answers

Independent variable

Type of food sample being tested

Dependent variable

Colour change in each test

Controlled variables

Volume of reagent, volume of food sample, temperature of water bath

✓Reducing sugar (glucose): Benedict's → brick red/orange (heat required)

✓Starch: iodine solution → blue-black

✓Protein: biuret reagent → purple/violet

✓Lipid: ethanol emulsion test → milky white emulsion

✓Negative results: Benedict's = blue, iodine = orange-brown, biuret = blue, emulsion = clear

✗Getting positive result colours wrong — must be exact (brick red, not just red)
✗Adding biuret reagents in wrong order — NaOH must go in first
✗Not heating Benedict's test — it won't change colour without heat